1. Field of the Invention
The present invention relates to a money screening method and a unit, and more particularly to a money screening method and a unit that can prevent the acceptance of foreign money or counterfeit money which material and outer diameter are very similar to genuine money, and can decrease the ratio of counterfeit money acceptance caused by the trial of continuously entering counterfeit money.
2. Description of the Related Art
Generally a money screening unit used for a vending machine, a money changing machine and service equipment is configured so as to sort coins entered from a coin slot into genuine coins and counterfeit coins, and to accept the screened genuine coins after sorting them by the type of money.
For sorting of coins, a sensor, which is installed on a coin passage for guiding a coin entered from the coin slot to a coin sorting section, detects such features as the material and shape of the coin, and this detection result becomes a base for sorting.
An example of the sensor for detecting features of a coin has a structure that a coil is positioned at one side of the coin passage, and an oscillation circuit is created including this coil. This sensor utilizes the change of inductance of the coil caused by a coin when the coin passes by the coil, and acquires information on the coin that passes by detecting changes of oscillation frequency.
Another example of the sensor has a structure that an oscillation coil which is excited by exciting current with specified frequency is positioned at one side of the coin passage, and a receiving coil is placed at the other side. This sensor utilizes a change of mutual coupling coefficient (magnetic coupling coefficient) between the oscillation coil and the receiving coil caused when a coin passes between the oscillation coil and the receiving coil, and acquires information on the coin that passes by detecting the change of output voltage of the receiving coil.
Inductance or mutual coupling coefficient, which are changed by passing of a coin, differ depending on the material of the coin, therefore, the material of the coin can be detected by the output whichever type of the above described sensors is used, and if oscillation frequency or exciting frequency is low, the surface material of the coin can be detected, whereas if oscillation frequency or exciting frequency is high, the internal material of the coin can be detected.
Outer diameter of a coin can be detected by adjusting the location of the sensor that is placed at the coin passage, because the height (area) of a coin which passes the coin passage differs depending on the diameter, therefore if the sensor is placed at a specified height, output becomes different depending on the coin that passes.
Generally, a conventional coin screening unit has the above described sensor for detecting material and outer diameter of a coin, and uses one or more sensors depending on the application.
In a conventional coin screening unit, however, genuineness of an entered coin is judged by material and outer diameter of the coin, therefore a coin which has a very similar material and outer diameter as a genuine coin, such as a foreign coin, is accepted as a genuine coin, and actual crimes using this shortcoming occur frequently.
Also when the above sensor is used for detecting money, the detection result varies even among the same type of money due to contamination of the coin and other factors, therefore an upper limit and lower limit are set in judgment data for sorting genuine money and counterfeit money, and money is judged as genuine when the detection result is within this range.
As a consequence, sorting of genuine money and counterfeit money is not always successful, and counterfeit money may be erroneously accepted as genuine, and even if the acceptance rate of counterfeit money is several percent or less, a counterfeit money may be accepted as genuine by the trial of continuously entering the counterfeit coin.
Particularly in the case of coins, there are many foreign coins which have similar material, outer diameter, and thickness, and crimes of stealing money and objects by altering such foreign coins frequently occur these days.
If a more strict sorting standard between genuine money and counterfeit money is set to prevent the acceptance of counterfeit money, then a slightly contaminated genuine money will be judged as counterfeit, which as a result will decrease functions of the money screening unit.